1. Field of the Invention
This invention relates to displacing hydrocarbon from subterranean formations and more particularly to improving the injectivity profile and/or vertical conformance of the formation.
Description of the Prior Art
Heterogeneous hydrocarbon bearing subterranean formations, i.e., formations having relatively high permeability zones and relatively lesser permeability zones, are difficult to effeciently flood by secondary and/or tertiary recovery processes. The highly permeable zones tend to "thieve" the displacement and/or drive fluids of such processes. When all, or a substantial portion, of the displacement and/or drive fluids flow through the relatively high permeability zones and avoid the lesser permeability zones, fingering and premature breakthrough of the fluids occurs resulting in decreased sweep efficiency of the secondary or tertiary floods.
To increase the efficiency of formation flooding processes, it has been previously suggested to "bridge" the more permeable zones to cause plugging or partial plugging of the relatively high permeability zones. This forces subsequently injected displacement and/or drive fluids into the lesser permeability zones. Previously suggested plugging agents include cement, plastics, coal tar products and by-products, cotton seed hulls, various organic compounds, etc. Particularly attractive plugging agents include high molecular weight polymers, and crosslinked products thereof. U.S. Pat No. 3,973,629 to Knight, et al teaches radiation induced copolymerization of acrylamide and/or methacrylamide with acrylic acid, methacrylic acid and/or salts thereof to provide polymers which are particularly useful for this purpose. U.S. Pat. No. 3,926,258 to Hessert, et al teaches the use of polyacrylamide, polysaccharide and/or cellulosic polymers with multivalent metal ions, a complexing agent and a reducing agent for such purposes. Other U.S. patents teaching the use of polymers in subterranean strata include U.S. Pat. Nos. 3,334,689 to McLaughlin; U.S. Pat. No. 3,421,584 to Eilers et al and U.S. Pat. No. 3,502,149 to Pence, Jr.